1. Field of the Invention
This invention relates to power transmissions and, specifically, to transmissions for bicycles.
2. Description of the Related Art
U.S. Pat. No. 589,266 to B. T. Nedland & C. Fredrickson describes a drive plate gear having separate gearing tracks. These gearing tracks were selectively engaged via drive shaft-attached pinion gears to change speed. In 1905, M. Jean-Baptiste Maynie of France patented a drive plate gear changing mechanism which incorporated six concentric gearing tracks engaged by a single drive shaft-attached pinion gear for ratio alterations. Variations on this shaft driven example were developed in 1945 by C. L. Hussey, and later by Marshall in 1990 who substituted the drive shaft with a chain drive but retained a gear change mechanism similar to those found in earlier accomplishments. These prior art models, however, proved to be costly to manufacture and provided for a relatively small number of gear ratios.
In U.S. Pat. No. 5,228,354 to Oosterwal et al teaches a gear change mechanism which utilizes both front and rear drive plate gears selectively engaged via axially movable pinion gears positioned at both the front and the rear of the drive shaft respectively adjacent their drive plate gear. A similar duality of drive plate gears is described by U.S. Pat. No. 5,342,075 to Williams. The invention of Williams, however, requires the cyclist to momentarily stop pedaling to change gear ratios.
The chain driven multi-speed derailleur system has proven itself over the years as lightweight, inexpensive to manufacture, and efficient. It also provides a wide range of gearing ratios selected via compact shifter devices and cables. The derailleur system does, however, have its disadvantages. One of the chief disadvantages of the derailleur system is its propensity to jam the chain between two sprockets while shifting. A second disadvantage of the derailleur system is its propensity to inappropriately shift by itself when used on rough terrain. Given the already large and ever increasing market of off-road bicycles (i.e., hybrids, Mountain bicycles) these difficulties have become more pronounced.
It is an object of this invention to provide a replacement for the popular derailleur chain drive system which is lightweight, quiet, efficient on all terrain and easily retrofit to existing bicycle designs.